Sound phenomena perplexed pre-scientific cultures lacking wave theory. Echo myths suggest virtual acoustic images were perceived as supernatural non-corporeal agents. Similarly, destructive interference can be modeled as virtual sound-attenuators casting acoustic shadows. Prehistoric cave paintings, canyon petroglyphs, megalithic monuments, and related myths of echo spirits and magic pipers are analyzed as evidence for ancient veneration rites tied to particular archaeological soundscapes. Just as virtual images appear within a mirror due to light reflection, virtual sound sources can seem to originate deep within a cliff due to sound reflection. Modern ray tracing modeling takes advantage of the fact that sound reflections from a surface are mathematically identical to sound waves emanating from virtual acoustic sources behind the reflecting plane. Myths around the world attest to beliefs that echoes were spirit voices calling out from rocks. Acoustic measurements support the hypothesis that ancient rock art locations were deliberately chosen for their sound reflection characteristics, and decorated with images that relate to the echo spirits believed to dwell there. In a similar way, sound attenuation caused by destructive wave cancellation from two sound sources can be misperceived as acoustic shadows. Interference patterns can be modeled by virtual sound-blocking objects perturbing the ambient sound. To people unaware of wave cancellation and reinforcement, the pattern of dead zones alternating with loud zones would have been completely mysterious, hence magical. Experiments with two flutes demonstrate that blindfolded participants can misinterpret the interference patterns as acoustic shadows cast by a ring of "pillars" similar to Stonehenge. This auditory illusion of unseen massive objects can be categorized as delusional perception, in which correctly sensed physical phenomena were given some additional interpretational significance. Myths of walls of air forming invisible towers, and two magic pipers who caused the formation of stone rings, provide additional clues. Measurements of the actual acoustic shadows radiating outward from Stonehenge are quantitatively and geometrically similar to a two point sound wave interference pattern. These data support the new theory that sound wave interference patterns were attributed to massive invisible objects, and that this “vision” of a ring of magic stones served as a blueprint for Stonehenge.

See http://sites.google.com/site/rockartacoustics/ for details including acknowledgements, photos and sound clips.